1. Field of the Invention
The present invention applies to radio communications systems in which several remote terminals communicate voice or data with a base station and, in particular, to such systems in which the base station selects channels to be used by the remote terminals for random access.
2. Description of the Prior Art
Mobile radio communications systems such as cellular voice radio systems typically have a base station available for use by mobile remote terminals, such as cellular telephones or wireless web devices. The base station typically transmits a broadcast channel (BCH). The BCH is broadcast to all remote terminals whether they are registered on the network or not and informs the remote terminals about the network. In order to access the network, a remote terminal must normally tune to and listen to the BCH before accessing the network. A remote terminal will typically scan a range of likely frequencies when it wants to access the network until it finds the strongest BCH, it will then use the information in the BCH to access the network.
The BCH is typically filled with data about the network in order to reduce the amount of information that must be transmitted to any particular remote terminal in the accessing, registering, authenticating or logging-on process. As a result, after registration, the remote terminal does not require any further information other than a specific channel assignment from the already known channel set in order to initiate a call.
The broadcast channel is typically transmitted at a relatively high power level so that any remote terminal in any location within the range of the base station can receive it clearly. The high power level and the high data rate in combination make it likely that the broadcast channel will interfere with other traffic channels of the radio communications system. When there are several different base stations transmitting on one or more broadcast channels, the possibility of and amount of interference is greater.
The present invention reduces the interference caused by the broadcast channel. This allows less of the channel resources to be dedicated to the broadcast channel and more of the channel resources to be dedicated to the traffic channels. In one embodiment, the broadcast channel is transmitted to all remote terminals that enter within the range of the base station while other communications are transmitted directly to the intended remote terminal on a channel that creates much less interference with other remote terminals. In such an embodiment, the present invention, by transmitting less data on the broadcast channel and more data on a specifically directed channel, reduces broadcast channel interference still more.